U.S. patent application number 11/702111 was filed with the patent office on 2007-08-16 for voltage balancer device for battery pack.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Tetsuya Kobayashi.
Application Number | 20070188138 11/702111 |
Document ID | / |
Family ID | 38367696 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070188138 |
Kind Code |
A1 |
Kobayashi; Tetsuya |
August 16, 2007 |
Voltage balancer device for battery pack
Abstract
A voltage balancer device has a plurality of discharge paths.
Each pair of the discharge paths correspond to each secondary
battery unit. Each of a pair of the discharge paths has a
resistance of a different value. Discharging the voltage of each
secondary battery unit is at first performed through the discharge
path of a smaller resistance value. The voltage balancer device
switches the currently used discharge path to another discharge
path having a large resistance value at the time the voltage of the
secondary battery unit nearly equal a desired voltage.
Inventors: |
Kobayashi; Tetsuya;
(Anjo-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
38367696 |
Appl. No.: |
11/702111 |
Filed: |
February 5, 2007 |
Current U.S.
Class: |
320/119 |
Current CPC
Class: |
H02J 7/0063 20130101;
H02J 7/0019 20130101; Y02T 10/7055 20130101; Y02T 10/70 20130101;
H02J 7/0014 20130101 |
Class at
Publication: |
320/119 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2006 |
JP |
2006-038851 |
Oct 19, 2006 |
JP |
2006-285231 |
Claims
1. A voltage balancer device, for a battery pack composed of a
plurality of secondary battery units connected in series,
configured to discharge a voltage of the secondary battery unit to
a desired voltage for voltage adjustment between the secondary
battery units, comprising: a discharge path connected in parallel
to and placed per secondary battery unit; and control means
configured to limit a current flowing through the discharge path so
that an actual current flowing through the discharge path at the
desired voltage becomes lower than a current at the desired voltage
determined on a straight line between an origin regarding a voltage
of both ends of the discharge path and a current flowing through
the discharge path and an actual value of the current at a
beginning of the discharging of the secondary battery unit.
2. The voltage balancer device according to claim 1, wherein the
control means has variable resistance means capable of increasing a
resistance value of the discharge path through which the discharge
current flows according to decreasing of the voltage of each
secondary battery unit.
3. The voltage balancer device according to claim 2, wherein each
discharge path comprises a resistance and a switching element
capable of switching an electrical on-off connection of the
discharge path, and the variable resistance means selects the
discharge path to be used for the discharging according to the
state of the switching element under the control of the control
means.
4. The voltage balancer device according to claim 1, wherein the
discharge path comprises a switching element, and the control means
comprises an operational amplifier, and one input terminal of the
operational amplifier is connected to a connection node between the
resistance and the switching element, and a voltage of more than 0V
is applied to the other input terminal of the operational
amplifier.
5. The voltage balancer device according to claim 4, further
comprises switch means configured to switch the electrical
connection between the output terminal of the operational amplifier
and an activation control terminal of the switching element, and
the control means controls the switching means in order to
electrically connects the output terminal of the operational
amplifier to the activation control terminal of the switching
element in order to adjust the voltage of the secondary battery
unit.
6. The voltage balancer device according to claim 4, wherein the
control means applies a voltage equal to an ordinary-using voltage
of the battery pack to the other input terminal of the operational
amplifier
7. The voltage balancer device according to claim 1, wherein each
discharge path connects in parallel to corresponding secondary
battery unit, and each discharge path comprises; a switching
element configured to switch electrical connection/non-connection
of each discharge path; and a constant current discharging means,
wherein the control means activates the switching element in order
to select the discharge path connecting the activated switching
element for discharging.
8. A voltage balancer device, for a battery pack composed of a
plurality of secondary battery units connected in series,
configured to discharge to a desired voltage a voltage of each
secondary battery unit or a voltage of a group composed of several
secondary battery units in order to adjust the voltage of each
secondary battery unit, comprising discharge paths, each discharge
path being connected in parallel to and placed at each secondary
battery unit, wherein each discharge path comprises a switching
element capable of switching an electrical on-off connection of the
discharge path.
9. A voltage balancer device, for a battery pack composed of a
plurality of secondary battery units connected in series,
configured to discharge to a desired voltage a voltage of each
secondary battery unit or a voltage of a group composed of several
secondary battery units in order to adjust the voltage of each
secondary battery unit, comprising: a discharge path equipped with
a switching element capable of switching an electrical on-off
connection of the discharge path, and each discharge path being
connected in parallel to and placed per secondary battery unit; and
an operational amplifier whose output terminal being connected to
an activation control terminal of the switching element, wherein
one input terminal of the operational amplifier is connected to a
connection node between the resistance and the switching element,
and a voltage of more than 0V is applied to the other input
terminal of the operational amplifier.
10. The voltage balancer device for a battery pack according to
claim 8, wherein the discharge path further comprises a constant
current discharge means connected to the switching element in
series.
11. The voltage balancer device for a battery pack according to
claim 8, wherein the discharge path further comprises a resistance
connected to the switching element in series.
12. A voltage balancer device, for a battery pack composed of a
plurality of secondary battery units connected in series,
configured to discharge to a desired voltage a voltage of each
secondary battery unit or a voltage of a group composed of some
secondary battery units in order to adjust the voltage of each
secondary battery unit, comprising: discharge paths, each discharge
path being connected in parallel to and placed at the corresponding
secondary battery unit; and control means configured to limit an
actual current flowing through the discharge path when the voltage
of the corresponding secondary battery unit becomes equal to a
desired voltage by changing a change rate of the current flowing
through the discharge path corresponding to the change of the
voltage of the secondary battery unit.
13. The voltage balancer device for a battery pack according to
claim 12, wherein the control means comprises variable resistance
means capable of increasing a resistance value according to
decreasing the voltage of the secondary battery unit.
14. The voltage balancer device for a battery pack according to
claim 13, wherein the discharge path is composed of a plurality of
the discharge paths connected in parallel to the secondary battery
units, each of the plural discharge paths has a resistance and a
switching element capable of switching an electrical on-off
connection of the discharge path, and the variable resistance means
selects the discharge path to be used for discharging by
controlling the switching element.
15. The voltage balancer device for a battery pack according to
claim 12, wherein the discharge path is composed of a plurality of
the discharge paths connected in parallel to the secondary battery
units, each of the plural discharge paths has a constant current
discharge means and a switching element capable of switching an
electrical on-off connection of the discharge path, and the control
means selects the discharge path to be used for discharging by
activating the switching element.
16. The voltage balancer device for a battery pack according to
claim 1, further comprising an average value detecting means
configured to detect an average value of the voltage of each
secondary battery unit, wherein the control means so controls that
the secondary battery unit whose voltage is over than the average
value is discharged through the discharge path corresponding to the
secondary battery unit.
17. The voltage balancer device for a battery pack according to
claim 8, further comprising an average value detecting means
configured to detect an average value of the voltage of each
secondary battery unit, wherein the control means so controls that
the secondary battery unit whose voltage is over than the average
value is discharged through the discharge path corresponding to the
secondary battery unit.
18. The voltage balancer device for a battery pack according to
claim 9, further comprising an average value detecting means
configured to detect an average value of the voltage of each
secondary battery unit, wherein the control means so controls that
the secondary battery unit whose voltage is over than the average
value is discharged through the discharge path corresponding to the
secondary battery unit.
19. The voltage balancer device for a battery pack according to
claim 12, further comprising an average value detecting means
configured to detect an average value of the voltage of each
secondary battery unit, wherein the control means so controls that
the secondary battery unit whose voltage is over than the average
value is discharged through the discharge path corresponding to the
secondary battery unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to and claims priority from
Japanese Patent Applications No. 2006-38851 filed on Feb. 16, 2006
and No. 2006-285231 filed on Oct. 19, 2006, the contents of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a voltage balancer device
for a battery pack composed of plural rechargeable secondary
battery units connected in series or for a set of some secondary
battery units adjacently connected, and the voltage balancer device
is capable of adjusting the voltage of a secondary battery unit by
discharging the voltage of the secondary battery unit.
[0004] 2. Description of the Related Art
[0005] For example, a battery pack composed of a plurality of
rechargeable secondary battery units (hereinafter, referred to as
secondary battery units) connected in series is mounted on various
types of vehicles such as a hybrid electric vehicle (HEV). In
particular, such a HEV has a possibility of varying a voltage of
each secondary battery mounted thereon. The voltage variation of
each secondary battery unit in the HEV is caused by residual
electric capacity of each secondary battery unit. The variation of
the residual electric capacity is caused by various conditions such
as the temperature variation and individual difference of each
secondary battery unit. In order to eliminate the voltage variation
between the secondary battery units, there is a conventional manner
of charging all of the secondary battery units forming a battery
pack by slightly over-discharging the battery pack composed of
nickel-hydrogen battery.
[0006] On the contrary, a lithium battery as a secondary battery
has a characteristic of promoting its deterioration by performing
over-charging. If the over-charging is performed for such a lithium
battery, the reliability thereof is drastically decreased.
[0007] Japanese patent laid open publication number JP2005-56654
has disclosed a voltage balancer device capable of adjusting the
voltage of each secondary battery unit by detecting the voltage of
each secondary battery unit and then by discharging a higher
voltage of the secondary battery unit through a discharge path
placed per secondary battery unit, where the discharge path is
connected to the secondary battery unit in parallel. However, when
an electric contact resistance of a connector that connects each
secondary battery unit with each discharge path in the conventional
voltage balancer device described above, the voltage of the
secondary battery unit is determined by the sum of the voltage drop
of the discharge path and the voltage drop of the connector.
Accordingly, even if the voltage of the discharge path is decreased
to a specified voltage level, the voltage value of the secondary
battery unit involves an error equal to the voltage drop of the
connector to the specified voltage value. It is necessary to
increase the resistance value of the discharge path in order to
reduce the amount of the error. However, this solution introduces
that the current flowing through the discharge path becomes small
and it takes a long period of time for discharging the secondary
battery unit.
[0008] In general, not only a battery pack composed of a plurality
of lithium battery units described above, but also a secondary
battery capable of adjusting the voltage of each secondary battery
unit by discharging a voltage of each secondary battery unit to a
specified voltage have a common problem in which controlling a
voltage of each secondary battery unit with high accuracy is
contrary to the adjusting period of time necessary for adjusting
the voltage of the secondary battery unit.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
voltage balancer device for a battery pack composed of a plurality
of rechargeable secondary battery units capable of adjusting a
voltage of each secondary battery unit to a desired voltage in a
short time by discharging a voltage of each secondary battery unit
to a specified voltage.
[0010] To achieve the above purposes, the present invention
provides a voltage balancer device, for a battery pack, configured
to discharge a voltage of the secondary battery unit to a desired
voltage for voltage adjustment between the secondary battery units.
The battery pack is composed of a plurality of rechargeable
secondary battery units connected in series. Hereinafter, each
rechargeable secondary battery unit is referred to as a secondary
battery unit for short. The voltage balancer device has a discharge
path per secondary battery unit and a control means. The discharge
path is connected in parallel to the secondary battery unit and the
discharge path is placed per secondary battery unit. The control
means is configured to limit a current flowing through the
discharge path so that an actual current flowing through the
discharge path at the desired voltage becomes lower than a current
at the desired voltage determined on a straight line between an
origin regarding a voltage of both ends of the discharge path and a
current flowing through the discharge path and an actual value of
the current at a beginning of the discharging of the secondary
battery unit.
[0011] When compared with a conventional configuration of a voltage
balancer device in which each discharge path is equipped with only
a resistance, the amount of an actual current flowing through the
discharge path is determined along a straight line. This straight
line connects the origin in a relationship between voltages at both
ends of the discharge path to a current flowing through the
discharge path at a discharge initiating time. In this case, it is
necessary to reduce the resistance value of the discharge path in
order to reduce the total period of time for performing the
discharging. However, the conventional configuration of the voltage
balancer device involves a drawback in which the occurrence of
increasing the resistance value of a connection node between the
discharge path and each secondary battery unit decreases the
voltage adjusting accuracy at the time the voltage of each
secondary battery unit is reduced to a desired voltage based on the
magnitude of the voltage drop of the discharge path.
[0012] On the contrary, in the configuration of the voltage
balancer device according to the present invention, the voltage
balancer device so controls that the actual current becomes lower
than the current value determined by the above straight line at the
time the voltage of the discharge path is nearly equal to the
desired voltage.
[0013] In the voltage balancer device according to another aspect
of the present invention, the control means has a variable
resistance means configured to increase a resistance value of the
discharge path through which the discharge current flows according
to decreasing of the voltage of each secondary battery unit. In
this configuration, it is possible to preferably limit the current
value which becomes near the desired voltage of each secondary
battery unit by increasing the resistance value of the discharge
path according to decreasing the voltage of each secondary battery
unit.
[0014] In the voltage balancer device according to another aspect
of the present invention, the discharge path is composed of plural
paths. Each path is composed of a resistance and a switching
element which is capable of switching an electrical on-off
connection of the discharge path. The variable resistance means
selects the discharge path to be used for discharging according to
the state of the switching element under the control of the control
means. In this configuration, it is possible to form each discharge
path with the switching element and the resistance, and thereby
possible to realize the variable resistance means by controlling
the operation of the switching element.
[0015] In the voltage balancer device according to another aspect
of the present invention, the discharge path has a switching
element and the control means has an operational amplifier. One
input terminal of the operational amplifier is electrically
connected to a connection node between the resistance and the
switching element. A voltage of more than 0V is applied to the
other input terminal of the operational amplifier. In the
configuration, the amount of the current flowing through the
discharge path becomes zero when the voltage at both ends of the
discharge path becomes equal to the voltage applied to the input
terminal of the operational amplifier. When compared with the
characteristic of the straight line which connects an origin
regarding the relationship (namely, along the straight line)
between the voltage at both ends of the discharge path and the
current flowing through the discharge path, the voltage of both
ends of the discharge path, the straight line obtained by the
voltage applied to both ends of the discharge path and the actual
current flowing through the discharge path provides a smaller
current value at a same voltage. It is thereby possible that an
actual current at the desired voltage becomes smaller than the
current value at the desired voltage determined by the straight
line which connects the origin of the voltage at both ends of the
discharge path and the current flowing through the discharge
path.
[0016] According to another aspect of the present invention, the
voltage balancer device further has a switch means configured to
switch the electrical connection between the output terminal of the
operational amplifier and an activation control terminal of the
switching element. The control means so controls in order to adjust
the voltage of the plural secondary battery units that the
switching means electrically connects the output terminal of the
operational amplifier to the activation control terminal of the
switching element. In this configuration, it is possible to avoid
the operation of discharging the secondary battery units through
the discharge path by the switching means when not requested.
[0017] In the voltage balancer device according to another aspect
of the present invention, the control means applies a voltage equal
to an ordinary-use voltage of the battery pack to the other input
terminal of the operational amplifier. In this configuration, it is
possible to set the amount of the current flowing through the
discharge path to zero when the voltage of both ends of the
discharge path becomes nearly equal to the desired voltage.
[0018] In the voltage balancer device according to another aspect
of the present invention, each discharge path connects in parallel
to each secondary battery unit, and each discharge path has a
switching element configured to switch electrical
connection/non-connection of each discharge path and a constant
current discharging means. The control means selects the path in
the discharge path by activating the switching element
corresponding to the discharge path to be used for discharging. In
this configuration, it is possible to change the amount of an
actual current flowing through the discharge path by switching the
currently-used discharge path with another discharge path.
[0019] According to another aspect of the present invention, the
voltage balancer device for a battery pack composed of a plurality
of secondary battery units connected in series is configured to
discharge to a desired voltage a voltage of each secondary battery
unit or a voltage of a group composed of some secondary battery
units in order to adjust the voltage of each secondary battery
unit. Each discharge path is connected in parallel to and placed at
each secondary battery unit. Each discharge path has a switching
element capable of switching an electrical on-off connection of the
discharge path. In this configuration, because the discharge path
is composed of a plurality of discharge paths, it is possible to
adjust the amount of the discharging current flowing through the
discharge path by switching the discharge path. This configuration
enables a large amount of the discharging current to flow at the
beginning period in the discharging and a small amount of the
discharging current to flow in a latter period in the discharging.
This can set the voltage of the secondary battery unit to a desired
voltage with high accuracy at high speed.
[0020] According to another aspect of the present invention, the
voltage balancer device for a battery pack composed of a plurality
of secondary battery units connected in series is configured to
discharge to a desired voltage a voltage of each secondary battery
unit or a voltage of a group composed of some secondary battery
units in order to adjust the voltage of each secondary battery
unit. The voltage balancer device has a discharge path and an
operational amplifier. The discharge path is equipped with a
switching element capable of switching an electrical on-off
connection of the discharge path. Each discharge path is connected
in parallel to and placed per secondary battery unit. An output
terminal of the operational amplifier is connected to an activation
control terminal of the switching element. In the voltage balancer
device, one input terminal of the operational amplifier is
connected to a connection node between the resistance and the
switching element, and a voltage of more than 0V is applied to the
other input terminal of the operational amplifier. In this
configuration, the amount of the current flowing through the
discharge path becomes zero when the voltage at both ends of the
discharge path is equal to the voltage applied to the other input
terminal of the operational amplifier. It is possible to easily
control the amount of the current flowing through the discharge
path when the voltage at both ends of the discharge path becomes
the desired voltage. This can set the voltage of the secondary
battery unit to a desired voltage with high accuracy at high
speed.
[0021] In the voltage balancer device according to another aspect
of the present invention, the discharge path further has a constant
current discharge means. In this configuration, it is possible to
change the actual current flowing through the discharge path by
switching the discharge path for use in the discharging. This
configuration enables a large amount of the discharging current to
flow at the beginning period of the discharging, and a small amount
of the discharging current to flow in a latter period of the
discharging. This can set the voltage of the secondary battery unit
to a desired voltage with high accuracy at high speed.
[0022] In the voltage balancer device according to another aspect
of the present invention, the discharge path further has a
resistance. In this configuration, it is also possible to change
the actual current flowing through the discharge path by switching
the discharge path for use in the discharging. This configuration
enables to flow a large amount of the discharging current at the
beginning period of the discharging, and to flow a small amount of
the discharging current in a latter period of the discharging. This
can set the voltage of the secondary battery unit to a desired
voltage with high accuracy at high speed.
[0023] According to another aspect of the present invention, a
voltage balancer device for a battery pack composed of a plurality
of secondary battery units connected in series is configured to
discharge to a desired voltage a voltage of each secondary battery
unit or a voltage of a group composed of some secondary battery
units in order to adjust the voltage of each secondary battery
unit. In particular, the voltage balancer device has discharge
paths and a control means. Each of the discharge paths is connected
in parallel to and placed at each secondary battery unit. The
control means is configured to limit an actual current flowing
through the discharge path when the voltage of the corresponding
secondary battery unit becomes equal to a desired voltage by
changing a change rate of the current flowing through the discharge
path corresponding to the change of the voltage of the secondary
battery unit. This configuration having the control means enables a
large amount of the discharging current to flow at the beginning
period of the discharging, and a small amount of the discharging
current to flow in a latter period of the discharging. This can set
the voltage of the secondary battery unit to a desired voltage with
high accuracy at high speed.
[0024] In the voltage balancer device according to another aspect
of the present invention, the control means has variable resistance
means capable of increasing a resistance value according to
decreasing the voltage of the secondary battery unit. This
configuration enables to preferably limit the amount of the current
flowing through the discharge path when the voltage of the
secondary battery unit reaches nearly equal to the desired voltage
by increasing the resistance value of the discharge path according
to the voltage drop of the secondary battery unit.
[0025] In the voltage balancer device according to another aspect
of the present invention, the discharge path is composed of a
plurality of the discharge paths connected in parallel to the
secondary battery units, each of the plural discharge paths has a
resistance and a switching element capable of switching an
electrical on-off connection of the discharge path, and the
variable resistance means selects the discharge path to be used for
discharging by controlling the switching element. In this
configuration, the discharge path is composed of a plurality of the
discharge paths and each discharge path is equipped with the
switching element and the resistance. It is thereby possible to
realize the variable resistance means by controlling the operation
of the switching element.
[0026] In the voltage balancer device according to another aspect
of the present invention, the discharge path is composed of a
plurality of the discharge paths connected in parallel to the
secondary battery units, each of the plural discharge paths has a
constant current discharge means and a switching element capable of
switching an electrical on-off connection of the discharge path,
and the control means selects the discharge path to be used for
discharging by activating the switching element. This configuration
enables to change the amount of the actual discharging current by
switching the discharge path to be used for discharging. It is
thereby possible to use the control means as the variable setting
means capable of switching the discharge path to be used for
discharging.
[0027] The voltage balancer device according to another aspect of
the present invention further has an average value detecting means
configured to detect an average value of the total voltages of the
secondary battery units. In the voltage balancer device, the
control means so controls that the secondary battery unit whose
voltage is more than the average value is discharged through the
discharge path corresponding to the secondary battery unit. It is
thereby possible to uniform all of the voltages of the secondary
battery units by discharging the voltage of the discharge path
whose voltage is over the average value of the voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] A preferred, non-limiting embodiment of the present
invention will be described by way of example with reference to the
accompanying drawings, in which:
[0029] FIG. 1 is a view showing an entire configuration of a
voltage balancer device for a battery pack according to a first
embodiment of the present invention;
[0030] FIG. 2 is a timing chart showing a discharging process of
discharging a voltage of a secondary battery unit under the control
of the voltage balancer device according to the first embodiment
shown in FIG. 1;
[0031] FIGS. 3A and 3B are views showing a relationship between a
discharge current and a voltage in different voltage adjustment
accuracy performed by the voltage balancer device of the first
embodiment shown in FIG. 1;
[0032] FIGS. 4A to 4D are views showing timing charts of the
discharging processes under the control of the voltage balancer
device of the first embodiment shown in FIG. 1;
[0033] FIGS. 5A to 5D are timing charts showing the discharging
process of a voltage balancer device according to a second
embodiment of the present invention;
[0034] FIG. 6 is a view showing an entire configuration of a
voltage balancer device for a battery pack according to a third
embodiment of the present invention;
[0035] FIG. 7 is a view showing a relationship between a discharge
current and a voltage in voltage adjustment accuracy under the
control of the voltage balancer device of the third embodiment;
[0036] FIG. 8 is a view showing an entire configuration of a
voltage balancer device for a battery pack according to a fourth
embodiment of the present invention;
[0037] FIGS. 9A to 9C are views showing timing charts of the
discharging process of the voltage balancer device of the fourth
embodiment shown in FIG. 8;
[0038] FIG. 10 is a view showing an entire configuration of a
voltage balancer device for a battery pack according to a fifth
embodiment of the present invention;
[0039] FIG. 11 is a view showing a relationship between a discharge
current and a voltage in a voltage adjustment accuracy under the
control of the voltage balancer device of the fifth embodiment;
and
[0040] FIG. 12 is a view showing an entire configuration of a
voltage balancer device for a battery pack according to a sixth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Hereinafter, various embodiments of the present invention
will be described with reference to the accompanying drawings. In
the following description of the various embodiments, like
reference characters or numerals designate like or equivalent
component parts throughout the several diagrams.
First Embodiment
[0042] A description will be given of a voltage balancer device 100
for a battery pack 10 according to the first embodiment of the
present invention with reference to FIG. 1 to FIGS. 4A, 4B, 4C, and
4D. The battery pack is composed of a plurality of rechargeable
secondary battery units B1 to Bn connected in series. The voltage
balancer device of the present invention is applicable to a hybrid
electric vehicle (HEV).
[0043] FIG. 1 is a view showing an entire configuration of the
voltage balancer device 100 for the battery pack 10 according to
the first embodiment of the present invention. As shown in FIG. 10,
the battery pack 10 is composed of a plurality of rechargeable
lithium secondary battery units B1 to Bn that are electrically
connected in series, where "n" is a natural number of two or more.
Hereinafter, the rechargeable lithium secondary battery units B1 to
Bn are referred to as secondary battery units b1 to Bn for
short.
[0044] The battery pack 10 acts as an electric power receptor
capable of recovering the electric power converted by and provided
from a vehicle alternator (not shown) mounted on a HEV when
applying breaks. Furthermore, the battery pack 10 acts as an
electric power supplier capable of supplying the accumulated
electric power to a vehicular battery of 12 Volts for example,
through a DC-DC converter. Still furthermore, the battery pack 10
acts as an electric power source capable of assisting an engine
mounted on the HEV when accelerating the driving speed of the
HEV.
[0045] In the configuration of the first embodiment, discharge
paths 20 and 30 are formed. The secondary battery units B1 to Bn
are electrically connected in parallel to a pair of the discharge
path 20 and the discharge path 30 through a corresponding connector
C. The discharge path 20 is equipped with a series circuit
consisting of a resistance 21 and a switching element 22.
Similarly, the discharging path 30 is equipped with a series
circuit consisting of a resistance 31 and a switching element 32.
Those series circuits are electrically connected to the secondary
battery units B1 to Bn through the connectors C.
[0046] Voltage detectors 40 are electrically connected in parallel
to the discharge paths 20 and 30. Each voltage detector 40 detects
a voltage between both end terminals of each secondary battery B1
to Bn. The voltage detector 40 outputs a detection result to a
voltage comparison unit 50 (as control means). When receiving the
detection result from each voltage detector 40, the voltage
comparison unit 50 controls the operation of the switching elements
22 and 32 based on the detection result received.
[0047] For more detailed explanation, the voltage comparison unit
50 as the control means calculates an average value of the voltages
of the secondary battery units B1 to Bn transferred form the
voltage detectors 40, and provides an instruction to the secondary
battery units having a voltage higher than the calculated average
value in order to discharge those secondary battery units B1 to Bn.
It is thereby possible for all of the secondary battery units B1 to
Bn to have a same voltage level.
[0048] FIG. 2 is a timing chart showing a discharging process
performed by the voltage balancer device 100 according to the first
embodiment shown in FIG. 1. The case shown in FIG. 2 uses a simple
model in which the number of the secondary battery units is only
two for the convenience of explanation.
[0049] In FIG. 2, the solid line designates a voltage of each
secondary battery, and the alternate long and short dash line
denotes an average value of the voltage of the two secondary
battery units. As shown in FIG. 2, when the discharging is
initiated at time t1, the voltage of the secondary battery unit
larger than the average voltage value is decreased to the average
voltage value. According to the voltage decreasing, the average
voltage value is also decreased. When the voltage of the secondary
battery unit becomes equal to the average voltage value at time t2,
the discharging process is completed.
[0050] When the resistance of the part other than the discharge
paths 20 and 30 in a closed loop circuit consisting of the
secondary battery B1 to Bn and the discharge paths 20 and 30 is
increased, for example, when a contact resistance of the connector
C is increased, the magnitude of the voltage drop of that part
cannot be disregarded during the discharging process. That is, when
the secondary battery units B1 to Bn are discharged through the
discharge path 20 when the contact resistance of the connector C is
increased, the sum of the voltage drop of the resistance 21 and the
voltage drop of the contact resistance of the connector C becomes
equal to the voltage of each of the secondary battery units B1 to
Bn.
[0051] On the contrary, the voltage detector 40 detects in fact the
voltage between both ends of the discharge path 20 as the voltage
of the secondary battery units B1 to Bn. This means that the
voltage of the secondary battery units B1 to Bn detected by the
voltage detector 40 includes the error component obtained by the
voltage drop of the contact resistance of the connector C. In order
to eliminate or reduce the error component as large as possible, it
is preferred to increase the resistance value of both of the
discharge paths 20 and 30 because the magnitude of the voltage drop
of the contact resistance of the connector C becomes a negligibly
small value when compared with the magnitude of the voltage drop of
the discharge paths 20 and 30. However, this case accompanies or
requires a long period of time for discharging the voltage of the
secondary battery units B1 to Bn through the discharge paths 20 and
30.
[0052] FIG. 3A shows a relationship between a voltage of each of
the discharge paths 20 and 30 and a discharge current flowing
through each of the discharge paths 20 and 30 with a small
resistance value. FIG. 3B shows a relationship between a voltage of
each of the discharge paths 20 and 30 and a discharge current
flowing through each of the discharge paths 20 and 30 with a large
resistance value. In FIGS. 3A and 3B, the alternate long and short
dash line designates the voltage at both end terminals of the
secondary battery units B1 to Bn, and the solid line denotes the
voltage at the both ends of the discharge paths 20 and 30.
Reference character V0 indicates the voltage of the secondary
battery units B1 to Bn at the beginning time of the discharging,
and V1 denotes a desired voltage of the secondary battery units B1
to Bn.
[0053] As shown in FIGS. 3A and 3B, the small resistance value of
the discharge paths 20 and 30 enables to increase the current
flowing through the discharge paths 20 and 30. However, the voltage
of the secondary battery units B1 to Bn takes the sum of the
desired voltage Va and an error component .DELTA.V1 (see FIG. 3A)
when the voltage at both end terminals of the discharge paths 20
and 30 reaches a desired voltage value Va.
[0054] On the contrary, in case of a large resistance value of the
discharge paths 20 and 30, the voltage of the secondary battery
units B1 to Bn takes the sum of the desired voltage Va and an error
component .DELTA.V2 (see FIG. 3B) when the voltage at both end
terminals of the discharge paths 20 and 30 reaches the desired
voltage value Va. The error component .DELTA.V2 shown in FIG. 3B is
smaller than the error component .DELTA.V1 shown in FIG. 3A. If the
resistance of the discharge paths 20 and 30 becomes high, it takes
a long time to perform the discharge because the amount of current
flow becomes small, namely, the maximum current value I02 of the
case shown in FIG. 3B is larger than the maximum current value I01
of the case shown in FIG. 3A (I02>I01).
[0055] In order to solve the above drawback, the voltage balancer
device 100 according to the first embodiment switches the discharge
paths. For more detailed explanation, the resistance value 31
mounted on the discharge path 30 is larger than the resistance
value 21 mounted on the discharge path 20. The voltage balancer
device 100 of the first embodiment uses the discharge path 20 in
the beginning discharging period, then switches the currently-used
discharge path 20 with the other discharge path 30, and uses the
discharge path 30 in the latter discharging period. FIG. 3A shows
the discharging process only through the discharge path 20, and
FIG. 3B shows the discharging process only through the discharge
path 30. The current has the current value I01 in the beginning
discharging period (see FIG. 3A), and the current has the current
value I02 in the latter discharging period (FIG. 3B). It is thereby
possible for the small current value I2 to flow when the voltage
detected by the voltage detector 40 becomes the desired voltage
value Va, wherein the current value I2 is smaller than the current
value I1 using the discharge path 20.
[0056] FIGS. 4A to 4D are views, each showing a timing chart of the
discharging process of the voltage balancer device 100 of the first
embodiment shown in FIG. 1. FIG. 4A shows the operation of the
switching element 22 in the discharge path 20. FIG. 4B shows the
operation of the switching element 32 in the discharge path 30.
FIG. 4C shows the resistance variation of the discharge path
through which the voltage is currently discharged. FIG. 4D shows
the voltage variation detected by the voltage detector 40.
[0057] As shown in FIGS. 4A to 4D, when the switching element 22 is
turned on at time t11, the resistance of the discharge path 20
becomes the resistance value of the resistance 21. The discharging
is thereby initiated. The voltage detected by the voltage detector
40 is thereby decreased. At time t12, the voltage comparison unit
50 as the control means so controls that the switching element 22
is turned off and the switching element 32 is turned on instead.
The resistance value of the discharge path 30 through which the
discharging is performed is thereby increased. Because this
increases a ratio of the voltage drop of the discharge path 30 to
the voltage drop of the entire closed loop circuit including the
secondary battery units B1 to Bn, the voltage is temporarily
increased at time t12. After this, the voltage detected by the
voltage detector 40 is decreased by performing the discharging
through the discharge path 30. Then, when the voltage becomes the
desired voltage value at time t13, the voltage comparison unit 50
so controls that the switching element 32 is turned off. The
discharging process is thereby completed.
[0058] According to the voltage balancer device 100 of the first
embodiment described above, the voltage comparison device 50 as the
control means so controls that the discharge path 20 is switched to
the discharge path 30 when the voltage detected by the voltage
detector 40 is nearly equal to the desired voltage Va.
[0059] In a concrete example, the desired voltage Va of a lithium
battery takes a range of 3.0V to 4.0V and preferably takes
approximately 3.6 V in normal use. Further, the discharge path 20
is switched to the discharge path 30 when the voltage detected by
the voltage detector 40 is within a range of 3.6V to 3.7V, for
example.
[0060] It is thereby possible to limit the amount of discharge
current when the voltage detected by the voltage detector 40 is
nearly equal to the desired voltage Va, and also possible for the
voltage detector 40 to accurately detect the voltage of the
secondary battery units B1 to Bn. The voltage balancer device 100
of the first embodiment enables accurate control of the secondary
battery units B1 to Bn to a desired voltage.
[0061] Accordingly, the voltage balancer device 100 of the first
embodiment has the effects (1), (2), and (3).
[0062] (1) The resistance value of the discharge path is increased
according to the magnitude of the voltage drop of the secondary
battery units B1 to Bn. This enables to efficiently limit the
current value when the voltage of the secondary battery units B1 to
Bn is nearly equal the desired voltage.
[0063] (2) The discharge paths 20 and 30 are equipped with the
resistances 21 and 31 of different resistance values, respectively.
The discharge path is switched with another discharge path by
operating the switching elements 22 and 32 in the discharge paths
20 and 30, respectively. It is thereby possible to change the
resistance value of the discharge path through which the voltage of
the secondary battery units B1 to Bn is currently discharged.
[0064] (3) Each voltage of the secondary battery units B1 to Bn is
detected, and the average value of the detected voltages is
calculated, and the voltages of the secondary battery units which
are higher than the calculated average value are discharged in
order to uniform the voltages of all of the secondary battery units
B1 to Bn.
Second Embodiment
[0065] Hereinafter, a description will be given of the voltage
balancer device according to the second embodiment with reference
to FIGS. 5A to 5D. The voltage balancer device according to the
second embodiment is equal in configuration to the voltage balancer
device 100 of the first embodiment shown in FIG. 1, the discharging
operation of the voltage balancer device 100 according to the
second embodiment is different from that of the first embodiment.
That is, in the voltage balancer device of the second embodiment
performs three steps for discharging. The primary discharging step
is performed using both of the discharge paths 20 and 30 connected
in parallel. The secondary discharging step is performed only using
the discharge path 20, and the final discharging step is performed
only using the discharge path 30.
[0066] FIGS. 5A to 5D are views showing the timing charts of the
discharging processes under the control of the voltage balancer
device 100 according to the second embodiment of the present
invention. Those timing charts shown in FIGS. 5A to 5D correspond
to the timing charts shown in FIG. 4A to 4D, respectively.
[0067] As shown in FIG. 5A to 5D, the discharge is initiated when
both of the switching elements 22 and 32 are turned on at timing
t21. The voltage comparison unit 50 as the control means so
controls that the switching element 32 is turned off and the
switching element 32 is not changed, namely, still turned on at
timing t22, where the voltage detected by the voltage detector 40
is nearly equal the desired voltage Va.
[0068] Because the resistance value of the discharge path for use
in the discharging is thereby increased, a ratio of the voltage
drop of the discharge path to the voltage drop of the entire closed
loop circuit including the secondary battery units B1 to Bn is
increased. The voltage detected by the voltage detector 40 is
thereby increased at time t22. After this, the voltage drops again,
and at timing t23 where the voltage is further nearly equal the
desired voltage Va when compared with the voltage at time t22, the
voltage comparison unit 50 so controls that the switching element
22 is turned off and the switching element 32 is turned on instead.
Because this switching increases the resistance value of the
discharge path for use in the discharging, the ratio of the voltage
drop of the discharge path to the total voltage drop of the closed
loop circuit including the secondary battery units B1 to Bn. At
time t23, the voltage detected by the voltage detector 40 is
thereby increased. When the voltage is decreased again to the
desired voltage Va, the voltage comparison unit 50 so controls that
the switching element 22 is turned off. The discharging is thereby
completed.
[0069] As described above in detail, the voltage balancer device
100 according to the second embodiment further has the following
effect (4) in addition to the effects (1) to (3) of the voltage
balancer device of the first embodiment.
[0070] (4) It is possible to form the discharge path having a
smaller resistance value by using both of the discharge paths 20
and 30 connected in parallel.
Third Embodiment
[0071] Hereinafter, a description will be given of the voltage
balancer device 300 according to the third embodiment with
reference to FIG. 6 and FIG. 7.
[0072] FIG. 6 is a view showing an entire configuration of the
voltage balancer device 300 for the battery pack 10 according to
the third embodiment. The battery pack 10 is composed of a
plurality of rechargeable secondary battery units B1 to Bn. The
voltage balancer device 300 of the third embodiment is basically
equal to that of the first embodiment. The difference between the
third embodiment and the first embodiment will be mainly described
later. In the following explanation, the components of the voltage
balancer device 300 of the third embodiment which are the same as
those of the first embodiments are designated with the same
numbers.
[0073] In the configuration of the voltage balancer device 300
shown in FIG. 6, each discharge path 20 corresponds to each of the
secondary battery units B1 to Bn, and each discharge path 20 is
connected in parallel to each secondary battery unit.
[0074] Through a switch 60, an output terminal of an operation
amplifier 62 is electrically connected to an on-state control
terminal of the switching element 22 or a base terminal of a
bipolar transistor as the switching element.
[0075] An inverse input terminal, designated by reference character
"-" in FIG. 6, of the operational amplifier 62 is electrically
connected to the connection node between the resistance 21 and the
switching element 22. A reference voltage Vref of a reference
voltage power source is applied to a non-inverse input terminal,
designated by reference character "+" in FIG. 6, of the operational
amplifier 62. The voltage comparison unit 50 transfers the
instruction to the switching element 60 which corresponds to the
secondary battery whose voltage is more than the minimum voltage of
the secondary battery units B1 to Bn. The secondary battery units
having the voltage of more than the minimum voltage are thereby
discharged.
[0076] FIG. 7 is a view showing a relationship between a discharged
current and a voltage detected by the voltage detector 40 when the
switching element 60 is turned on. In FIG. 7, the solid line shows
the change of the voltage detected by the voltage detector 40. The
voltage drops from the voltage Vo to the reference voltage Vref
designated by the solid line in FIG. 7. Because the current flow
can be limited near the reference voltage Vref, it is possible to
control the voltage of each of the secondary battery units B1 to Bn
with high accuracy when the desired voltage is near the reference
voltage Vref. In this case, the reference voltage Vref is a voltage
(for example, 3.6 V) corresponding to the residual capacity of each
of the secondary battery units B1 to Bn in an ordinary use range of
the battery pack. It is thereby possible to have the current value
of approximate zero which nearly equals the desired voltage.
[0077] On the contrary, in FIG. 7, the alternate long and short
dash line indicates the change of the voltage when zero voltage is
applied to the non-inverse input terminal of the operational
amplifier 62. In this case, the current is changed, just like the
case of the voltage balancer device 100 according to the first
embodiment shown in FIG. 1 in which the discharge path 20 is made
of the resistance 21 and a large amount of current flows when the
voltage is equal to the reference voltage Vref.
[0078] Accordingly, the voltage balancer device 300 of the third
embodiment having the above configuration has the following effects
(5), (6), and (7).
[0079] (5) In the voltage balancer device 300 of the third
embodiment, the output signal of the operational amplifier 62 is
transferred to the on-state control terminal of the switching
element 22 (namely, to the base terminal of the bipolar transistor
22) through the switch 60, and the inverse-input terminal
(designated by reference character "-" in FIG. 6) of the
operational amplifier 62 is connected to the connection node
between the resistance 21 and the switching element 22, and the
voltage of more than zero is applied to the non-inverse terminal
(designated by reference character "+" in FIG. 6) of the
operational amplifier 62. It is thereby possible to limit the
amount of the actual current when the voltage is near or equal to
the desired voltage, and thereby possible to control the voltage of
each of the secondary battery units B1 to Bn with high
accuracy.
[0080] (6) The voltage balancer device 300 according to the third
embodiment has the switch 60 capable of switching the on/off
electrical connection between the operational amplifier 62 and the
switching element 22, and the switch 60 is turned only when the
voltage control or adjusting between the secondary battery units B1
to Bn is requested. It is thereby possible to avoid the discharging
through the discharge path during the unnecessary voltage
adjustment.
[0081] (7) It is possible to perform the voltage control or
adjustment between the secondary battery units B1 to Bn at much
higher accuracy by applying the voltage for use in ordinary process
to the non-inverse input terminal (designated by reference
character "+" in FIG. 6) of the operational amplifier 62.
Fourth Embodiment
[0082] Hereinafter, a description will be given of the voltage
balancer device 400 according to the fourth embodiment with
reference to FIG. 8 and FIG. 9.
[0083] FIG. 8 is a view showing an entire configuration of the
voltage balancer device 400 for the battery pack according to the
fourth embodiment. The battery pack is composed of a plurality of
the rechargeable secondary battery units B1 to Bn. The voltage
balancer device 400 of the fourth embodiment is basically equal to
that of the first embodiment. The difference between the first
embodiment and the fourth embodiment will be mainly described
later. In the following explanation, the components of the voltage
balancer device 400 of the fourth embodiment which are the same as
those of the first embodiments are designated with the same
numbers.
[0084] As shown in FIG. 8, the discharge path 20 is placed in
parallel to each of the secondary battery units B1 to Bn. The
discharge path 20 is composed of the resistance 21 and a bipolar
transistor 23 connected in series. In the fourth embodiment, the
current flowing through the on-state control terminal (a base
terminal) of the bipolar transistor 23 is decreased in the latter
period in the discharging, not in the beginning period therein in
order to limit the amount of current flowing through the collector
and emitter of the bipolar transistor 23. In other words, the
current flowing through the collector and the emitter of the
bipolar transistor 23 is limited by controlling so that the voltage
detected by the voltage detector 40 becomes nearly equal the
desired voltage Va.
[0085] FIGS. 9A to 9C are views showing timing charts of the
discharging process under the control of the voltage comparison
unit 50 as the control means in the voltage balancer device 400 of
the fourth embodiment shown in FIG. 8. In particular, FIG. 9A shows
the current flowing through the base terminal of the bipolar
transistor 23, FIG. 9B shows the current flowing through the
discharge path 20, and FIG. 9C shows the voltage detected by the
voltage detector 40.
[0086] As shown in FIGS. 9A to 9C, the voltage comparison unit 50
activates the base terminal of the bipolar transistor 23 at timing
t31, so that the collector and the emitter of the bipolar
transistor 23 are electrically connected, namely, the current flows
between the emitter terminal and collector terminal of the bipolar
transistor 23. Thereby, the voltage detected by the voltage
detector 40 gradually drops.
[0087] At timing t32 when the voltage detected by the voltage
detector 40 becomes nearly equal the desired voltage Va, the
voltage comparison unit 50 controls so that the amount of current
flowing through the base terminal of the bipolar transistor 23 is
decreased. Simultaneously, it is preferred that the voltage
comparison unit 50 detects the voltage between the base terminal
and the emitter terminal of the bipolar transistor 23 and controls
the amount of the current flowing through the base terminal of the
bipolar transistor 23 according to this detected voltage. It is
thereby possible to limit the current flowing between the collector
terminal and the emitter terminal of the bipolar transistor 23 when
compared with the case using a fixed amount of a base current. This
configuration of the fourth embodiment enables that the voltage
detector 40 precisely detects the voltage of each of the secondary
battery units B1 to Bn. Further, it is possible that the base
current is set to zero in order to complete the discharging at
timing t33 when each of the secondary battery units B1 to Bn is
nearly equal the desired voltage Va.
[0088] The voltage balancer device 400 of the fourth embodiment
having the above configuration has the following effect (8).
[0089] (8) The voltage comparison unit 50 decreases the amount of
the current flowing through the base terminal of the bipolar
transistor 23 when the voltage detected by the voltage detector 40
is nearly equal the desired voltage Va. It is thereby possible to
limit the amount of the current flowing through the discharge path
20 when the voltage detected by the voltage detector 40 reaches the
desired voltage Va.
Fifth Embodiment
[0090] Hereinafter, a description will be given of the voltage
balancer device 500 according to the fifth embodiment with
reference to FIG. 10 and FIG. 11.
[0091] FIG. 10 is a view showing an entire configuration of the
voltage balancer device 500 for the battery pack 10 according to
the fifth embodiment of the present invention.
[0092] The voltage balancer device 500 of the fourth embodiment is
basically equal to that of the first embodiment. The difference
between the first embodiment and the fifth embodiment will be
mainly described later. In the following explanation, the
components of the voltage balancer device 500 of the fifth
embodiment which are the same as those of the first embodiments are
designated with the same numbers.
[0093] In the voltage balancer device 500 of the fifth embodiment
shown in FIG. 10, the discharge path 20 is composed of the
switching element 22 and a constant current diode 24 which are
connected in series. Further, the discharge path 30 is composed of
the switching element 32 and a constant current diode 34 which are
connected in series.
[0094] In the configuration of the voltage balancer device 500 of
the fifth embodiment, the constant current diodes 24 and 34 are so
formed that the output current Ia of the constant current diode 24
is greater than the output current Ib of the constant current diode
34, and the voltage comparison unit 50 as the control means
controls the on-off operation of the switching elements 22 and 32
in order to switch the discharge path.
[0095] FIG. 11 shows the discharging process performed by the
switching elements 22 and 32 under the control of the voltage
balancer device 500 according to the fifth embodiment. In FIG. 11,
the vertical line indicates the voltage detected by the voltage
detector 40 and the horizontal line indicates the discharge
current.
[0096] As shown in FIG. 11, in case that the discharging is
initiated when the voltage detected by the voltage detector 40
becomes the voltage V0, the voltage comparison unit 50 so controls
that the switching element 22 is turned on and the switching
element 32 is turned off. As a result, the discharging is performed
only through the discharge path 20, and the discharge current is
referred to as the output current Ia. Following, when the voltage
detected by the voltage detector 40 becomes nearly equal the
desired voltage Va, the voltage comparison unit 50 switches the
state of both of the switching elements 22 and 32, namely, the
voltage comparison unit 50 so controls that the switching element
22 is turned off and the switching element 32 is turned on. The
discharging is thereby performed only through the discharge path 30
and the discharge current becomes the output current Ib that is
smaller than the output current Ia. It is thereby possible to limit
the discharge current when the voltage detected by the voltage
detector 40 is near the desired voltage Va. In particular, it is
possible to decrease the actual discharge current when the voltage
detected by the voltage detector 40 is near the desired voltage Va
when compared with the current that is determined by the desired
voltage Va and the dashed line shown in FIG. 11 that connects the
origin and the discharge start point (Ia, V0).
[0097] The voltage balancer device 500 according to the fifth
embodiment of the above configuration has the following effect (9)
in addition to the effect (3) of the voltage balancer device 100 of
the first embodiment.
[0098] (9) The voltage balancer device 500 of the fifth embodiment
has the discharge paths 20 and 30 composed of the switching
elements 22 and 32 and the constant current diodes 24 and 34
connected in series. The voltage comparison unit 50 as the control
means switches the currently-used discharge path to the other
discharge path in order to select the discharge path to be newly
used by controlling the switching elements 22 and 32. It is thereby
possible to change the actual current flowing through the selected
discharge path in order to limit the amount of the current when the
voltage detected by the voltage detector 40 is nearly equal the
desired voltage Va.
Sixth Embodiment
[0099] Hereinafter, a description will be given of the voltage
balancer device 600 according to the sixth embodiment with
reference to FIG. 12.
[0100] FIG. 12 is a view showing an entire configuration of the
voltage balancer device 600 for the battery pack 10 according to
the sixth embodiment of the present invention.
[0101] The voltage balancer device 600 of the sixth embodiment is
basically equal to that of the first embodiment. The difference
between the first embodiment and the sixth embodiment will be
mainly described later. In the following explanation, the
components of the voltage balancer device 600 of the sixth
embodiment which are the same as those of the first embodiments are
designated with the same numbers.
[0102] As shown in FIG. 12, each of the secondary battery units B1
to Bn is composed of a group of n battery cells Bi1 to Bin
(i=1.about.m). For example, the secondary battery unit B1 is
composed of plural battery cells B11 to B1n as a block. The
discharge paths 20 and 30 are placed for each battery block. The
voltage detector 40 detects the voltage of each battery block. The
voltage comparison unit 50 controls the operation of the switching
elements 20 and 30 based on the detected voltage in order to
discharge the battery cells Bi1 to Bin (i=1.about.m) in the battery
block of a higher voltage. The manner how to control both the
discharge paths 20 and 30 in the sixth embodiment is equals to the
manner in the first embodiment.
[0103] It is preferred to have the discharging function per
secondary battery unit B1 to Bn like the first embodiment in
addition to the discharging function capable of performing the
discharging process per battery block.
[0104] According to the sixth embodiment of the present invention
as described above, it is possible to have the effects for the
secondary battery cells Bi1 to Bin in each battery block
corresponding to the effects of the first embodiment.
(Other modifications)
[0105] The first to sixth embodiments use a bipolar transistor as
the switching element 22. The present invention is not limited by
this configuration, for example, it is acceptable to use a MOS
transistor as the switching element 22 instead of the bipolar
transistor.
[0106] Further, each of the first to sixth embodiments uses the
average voltage as the desired voltage Va between the secondary
battery units B1 to Bn. The present invention is not limited by
this configuration, for example, it is possible to use the minimum
voltage between the secondary battery units B1 to Bn.
[0107] In the first embodiment, it is possible to use both the
discharge paths 20 and 30 during the beginning period in the
discharging, and to use one of the discharge paths 20 and 30 after
the latter period of the discharging. In this case, it is possible
to use the resistances 21 and 31 of a same resistance value.
[0108] Although the first and second embodiments use the discharge
paths 20 and 30, the present invention is not limited by this
configuration, for example, it is acceptable to use two or more
kinds of discharge paths.
[0109] Further, although the first and second embodiments use the
voltage comparison unit 50 as the control means that acts as the
resistance change means capable of increasing the resistance value
of the discharge path according to the decrease of the voltage of
the secondary battery unit, the present invention is not limited by
this configuration, for example, it is acceptable to have a single
discharge path equipped with a variable resistance unit for each of
the secondary battery units B1 to Bn placed in parallel, and to
have a variable resistance means capable of adjusting the
resistance value of the variable resistance means.
[0110] The third embodiment uses the voltage, corresponding to the
residual capacitance, to be applied to the non-inverse input
terminal of the operational amplifier 62. However, the present
invention is not limited by this configuration. For example, it is
sufficient to reduce the actual current value, at the desired
voltage actually detected by the voltage detector, rather than the
current value at the desired voltage that is determined by the
alternate long and short dashed line shown in FIG. 7 which connects
the origin of the voltage-discharge current line with the actual
value at the beginning period of the discharging, where the
voltage-discharge current line is detected by the voltage detector
40 by applying the voltage of more than zero to the non-inverse
input terminal of the operational amplifier 62.
[0111] It is thereby possible to detect the voltage of each of the
secondary battery units B1 to Bn with high accuracy because the
amount of the current can be limited when the detected voltage
reaches the desired voltage.
[0112] In the third embodiment, the voltage of a fixed level is
applied to the non-inverse input terminal of the operational
amplifier 62. However, the present invention is not limited by this
configuration. For example, it is possible to apply a variable
voltage to the non-inverse input terminal of the operational
amplifier 62. In this case, it is preferred to apply an optional
voltage to the non-inverse input terminal of the operational
amplifier. This enables to adjust the voltage of each of the
secondary battery units B1 to Bn to a desired voltage level with
high accuracy without incorporating the voltage detector 40.
[0113] The third embodiment uses the switch 60 as shown in FIG. 6.
However, the present invention is not limited by this
configuration. For example, it is possible to perform the voltage
discharging while avoiding that the voltage of each of the
secondary battery units B1 to Bn does not exceed the reference
voltage Vref without using the switch 60.
[0114] In the fifth embodiment, it is so controlled that the actual
discharge current value when the detected voltage becomes the
desired voltage Va is smaller than the current at the desired
voltage Va that is determined by the alternate long and short
dashed line shown in FIG. 7 which connects the origin (0, 0) to the
discharge initial point (Ia, V0). However, the present invention is
not limited by this configuration. For example, it is possible to
limit the amount of the discharge current near the desired voltage
Va without the above condition. It is possible to set the actual
voltage to the desired voltage with high accuracy in short time by
incorporating the plural discharge paths 20 and 30.
[0115] In addition, the fifth embodiment has the different output
currents of the constant current diodes 24 and 34. However, the
present invention is not limited by this configuration. For
example, it is possible to have the same output current of the
constant current diodes 24 and 34. In this case, it is also
possible to limit the discharge current near the desired voltage by
using both of the discharge paths 20 and 30 in the beginning period
of the discharging and then using only one of the discharge paths
20 and 30 at the latter period of the discharging.
[0116] In the fifth embodiment, it is acceptable to use two or more
discharge paths. Further, the constant current discharge means,
that is capable of discharging a constant current regardless of the
magnitude of the applied voltage, is made of a constant current
diode. However, the present invention is not limited by this
configuration. For example, it is acceptable to use a current
mirror circuit and the like as the constant current discharge means
instead of the constant current diode.
[0117] It is acceptable to mount the voltage balancer device for a
battery pack or a battery module according to the present invention
on another type of electric vehicles in addition to a hybrid
electric vehicle (HEV).
[0118] While specific embodiments of the present invention have
been described in detail, it will be appreciated by those skilled
in the art that various modifications and alternatives to those
details could be developed in light of the overall teachings of the
disclosure. Accordingly, the particular arrangements disclosed are
meant to be illustrative only and not limited to the scope of the
present invention which is to be given the full breadth of the
following claims and all equivalent thereof.
* * * * *